The present invention relates generally to a method and apparatus for measuring the height of a substrate, and more particularly, to a method and apparatus for measuring the height of a substrate in a dispensing system that dispenses viscous materials onto the substrate. The height measurement is used to ensure that a dispensing nozzle of the dispensing system is at a predetermined distance above the substrate prior to dispensing the material.
There are several types of prior art dispensing machines used for dispensing metered amounts of liquid or paste for a variety of applications. One such application is in the assembly of printed circuit boards or integrated circuit chips, wherein dispensing machines are used for encapsulating integrated circuits and/or for underfilling flip integrated circuit chips. Prior art dispensing systems are also used for dispensing dots or balls of liquid epoxy or solder onto circuit boards. The liquid epoxy or solder is used to connect components to the circuit boards. The dispensing systems described above include those manufactured and distributed by Camelot Systems Inc., the assignee of the present invention, under the name CAM/A LOT(copyright)).
In a typical dispensing system, a pump and dispenser assembly is mounted to a moving assembly for moving the pump and dispenser assembly along three mutually orthogonal axes (x, y, z), typically using servo motors controlled by a computer system or controller. To dispense a dot of liquid on a circuit board at a desired location, the pump and dispenser assembly is moved along the horizontal x and y axes until it is located over the desired location. The pump and dispenser assembly is then lowered along the vertical z-axis until the nozzle is at an appropriate height over the board. The pump and dispenser assembly dispenses a dot of liquid, is then raised along the z-axis, moved along the x and y axes to a next desired location, and lowered along the vertical z-axis to dispense a next liquid dot.
In these dispensing systems, it is critical that the distance between the dispensing nozzle and the circuit board be carefully maintained to ensure that the dot of material is properly dispensed onto the circuit board. Although the absolute location of the nozzle can be precisely controlled by the servo motors and the controller, the z-axis position at which the nozzle must be located to obtain the precise distance above the circuit board is variable because of variations in height among circuit boards that are to receive the dispensed material. Thus, the proper z-axis dispensing position of the nozzle for one circuit board may not be equal to the proper z-axis dispensing position of the nozzle for a second circuit board. Further, in addition to there being variations in height among circuit boards, the upper surface of each circuit board may have irregularities such that the height of a circuit board is different at one location on the circuit board than it is at another location on the circuit board.
In one prior art dispensing system, a touch probe, incorporated into the pump and dispenser assembly, is used to position the nozzle at the desired distance above a circuit board. The touch probe 20 will now be described with reference to FIGS. 1A, 1B and 1C, which show the touch probe 20 disposed over a circuit board 10. Each of FIGS. 1A, 1B and 1C show the touch probe 20 during a different stage of the positioning process.
The touch probe 20 includes a lower housing 22, a pneumatic actuator 24, and a cylinder 26 that extends from the pneumatic actuator to the lower housing. The pneumatic actuator is coupled to an air tube 18 which is coupled to a pressurized air source (not shown). The lower housing 22 is shown in a partially broken away view to show the position of the cylinder 26 within the lower housing. The cylinder 26 has a probe end 28 that during operation of the touch probe extends from the lower housing to contact the circuit board 10. Mounted on one side of the lower housing is a proximity sensor 36 that is implemented using an electromagnetic field to detect a metal target. The proximity sensor is electrically coupled to a controller (not shown) of the dispensing system. The cylinder 26 has a ring 30 made from stainless steel that can be readily detected by the proximity sensor 36.
The touch probe 20 operates in the dispensing system as follows. A circuit board to receive dispensed material at a number of dispensing locations on the top surface of the circuit board is loaded into the dispensing system. For each of the dispensing locations, the touch probe is used to determine the z-axis position of the pump and dispenser assembly that will result in the desired distance between the nozzle and the circuit board. It should be noted, however, that depending on the tolerance of the circuit board, the touch probe may measure the z-axis position at some number of dispensing locations less than the total number of dispensing locations. The touch probe 20, as shown in FIG. 1A, is positioned at a distance d1 above a first dispensing location of the circuit board 10. In FIG. 1, the cylinder 26 is shown in a retracted position such that the entire cylinder is contained within the lower housing 22. The cylinder 26 is held in the retracted position by a spring located in the pneumatic actuator 24. Once the touch probe 20 is in the position shown in FIG. 1A, the controller controls the pressurized air source to supply pressurized air to the pneumatic actuator 24 to actuate the touch probe. The pressurized air compresses the spring releasing the force exerted on the cylinder 26 by the spring, and allowing the cylinder to fall to an actuated position as shown in FIG. 1B.
Once the touch probe is in the actuated position, the controller controls the servo motors of the moving assembly to slowly lower the pump and dispenser assembly, thereby lowering the touch probe 20 which is attached to the pump and dispenser assembly. The controller continues to lower the touch probe until receiving an indication from the proximity sensor 36 that the ring 30 on the cylinder 26 is aligned with the proximity sensor (see FIG. 1C). Upon receipt of the indication from the proximity sensor, the controller stops the movement of the touch probe assembly, and stores the z-axis position of the pump and dispenser assembly. When the controller stops the movement of the pump and dispenser assembly, the lower housing 22 is at a distance d2 from the circuit board. The position of the touch probe on the pump and dispenser assembly is precalibrated such that when the lower housing is at the distance d2 from the circuit board, the nozzle of the pump and dispenser assembly is at the desired dispensing distance above the circuit board.
The calibration procedure described above is repeated for each of the dispensing locations on the circuit board to obtain the proper z-axis dispensing position for each dispensing location. The pump and dispenser assembly is then moved to each of the dispensing locations, positioned at the proper z-axis dispensing position previously determined using the touch probe, and material is dispensed onto the top surface of the circuit board.
There are drawbacks associated with the touch probe and calibration procedure described above. First, the procedure is relatively time consuming since at each dispensing location, the pump and dispenser assembly must be slowly lowered towards the circuit board. If the pump and dispenser assembly is moved too quickly, then any time delay associated with the detection of the ring 30 and the stopping of the servo motors will result in errors in determining the proper z-axis dispensing position. Even when the probe is moved relatively slowly, any delay in stopping the servo motors may still result in unacceptable error.
Embodiments of the present invention are directed to a method and apparatus for measuring the height of the surface of a substrate onto which material is to be dispensed by a dispensing system.
One embodiment of the present invention is directed to a dispensing system for dispensing material onto a top surface of a substrate. The dispensing system includes a housing, a dispensing apparatus that dispenses a metered quantity of material, and a measuring probe positionable over the substrate to measure. a distance from a reference point on the measuring probe to a location on the top surface of the substrate.
In an alternate version of the first embodiment, the measuring probe has an output to provide at least one measurement signal indicative of the distance from the reference point to the top surface of the substrate. The dispensing system further comprises a controller that receives the at least one measurement signal.
In another alternate version of the first embodiment, the measuring probe has a retracted state and an actuated state, and the measuring probe includes a probe end that in the retracted state is at a first distance from the reference point, and in the actuated state is at a second distance from the reference point.
In another alternate version of the first embodiment, the measuring probe has an input to receive a voltage signal, and the measuring probe is adapted to provide the at least one measurement signal in response to the voltage signal.
In another alternate version of the first embodiment, the measuring probe includes an actuator that in response to an actuation signal controls the measuring probe to be in one of the actuated state and the retracted state.
In another alternate version of the first embodiment, the dispensing system further includes a moving apparatus that positions the measuring probe along first, second and third orthogonal axes. The first and second axes are parallel to the top surface of the substrate and the third axes is perpendicular to the top surface of the substrate.
In yet another alternate version of the first embodiment, the controller of the dispensing system is programed to calculate the distance from the reference point of the measuring probe to the surface of the substrate based on the at least one measurement signal.
In another alternate version of the first embodiment, the controller is programmed to calculate the height of the substrate based on the at least measurement signal.
In another alternate version of the first embodiment, the dispensing apparatus has a dispensing nozzle having a dispensing end for dispensing the material, and the controller is programmed to calculate, based on the height of the substrate, a dispensing position on the third axis at which the nozzle end is at a predetermined distance from the top surface of the substrate.
In yet another alternate version of the first embodiment, the moving apparatus of the dispensing system is coupled to the dispensing apparatus to move the dispensing end to a position along the first, second and third axes. In this alternate version, the controller is coupled to the moving apparatus and is programmed to control the moving apparatus to move the dispensing end to the dispensing position on the third axis prior to dispensing material onto the substrate.
A second embodiment of the present invention is directed to a method for dispensing material onto a top surface of a substrate using a dispensing system having a dispensing apparatus at a dispensing distance from the top surface of the substrate. The method includes steps of loading a substrate onto a support plate on the dispensing apparatus, positioning a measuring probe above the substrate at a predetermined height above the support plate, measuring a distance between the measuring probe and the top surface of the substrate, positioning the dispensing apparatus at the dispensing distance above the top surface of the substrate, and dispensing material onto the substrate.
In an alternate version of the second embodiment, the measuring probe has a probe end, and the measuring probe has a retracted state and actuated state. In this alternate version, the method further includes steps of positioning the measuring probe, in the retracted state, above the substrate, and switching the probe from the retracted state to the actuated state, such that the probe end is positioned on the top surface of the substrate.
In another alternate version of the second embodiment, the measuring step includes steps of applying a primary voltage signal to the measuring probe, and receiving at least one secondary voltage signal from the measuring probe having signal characteristics indicative of the distance between the top surface of the substrate and the measuring probe.
In yet another alternate version of the second embodiment, the measuring probe is coupled to the dispensing apparatus, and the step of positioning the measuring probe at a predetermined height includes a step of positioning the dispensing apparatus at the predetermined height, and the step of measuring includes a step of maintaining the dispensing apparatus at the predetermined height during the measuring step.
A third embodiment of the present invention is directed to a dispensing system for dispensing material onto a top surface of a substrate. The dispensing system includes a housing, a dispensing apparatus that dispenses a quantity of material, and means for measuring the distance from a reference point on the dispensing system to a location on the top surface of the substrate.
In an alternate version of the third embodiment, the dispensing system further includes control means for positioning the dispensing apparatus along first, second and third orthogonal axes, wherein the first and second axes are parallel to the top surface of the substrate and the third axis is perpendicular to the top surface of the substrate.
In another alternate version of the third embodiment, the dispensing nozzle has a dispensing end for dispensing material and the means for positioning includes means for calculating a dispensing position on the third axis at which the dispensing end is at a predetermined distance from the top surface of the substrate.
In yet another alternate version of the third embodiment, the means for controlling includes means for moving the dispensing end to the dispensing position on the third axis prior to dispensing material onto the substrate.